U.S. patent application number 14/147653 was filed with the patent office on 2014-07-24 for zoom lens and image pickup apparatus including the same.
The applicant listed for this patent is CANON KABUSHIKI KAISHA. Invention is credited to Hideki Sakai.
Application Number | 20140204264 14/147653 |
Document ID | / |
Family ID | 51207402 |
Filed Date | 2014-07-24 |
United States Patent
Application |
20140204264 |
Kind Code |
A1 |
Sakai; Hideki |
July 24, 2014 |
ZOOM LENS AND IMAGE PICKUP APPARATUS INCLUDING THE SAME
Abstract
A zoom lens includes, in order from an object side to an image
side: a positive first lens unit; a positive second lens unit; and
an aperture stop disposed between the first and second lens units
and moving along a locus different from loci of the first and the
second lens units during zooming, the first and second lens units
being configured to change an interval therebetween during zooming,
the second lens unit including at least one positive lens and at
least one negative lens. A distance from a lens surface closest to
the object side in the entire system to the aperture stop at a wide
angle end, and a distance from the lens surface closest to the
object side in the entire system to a lens surface closest to the
object side in the second lens unit at the wide angle end are each
appropriately set.
Inventors: |
Sakai; Hideki; (Sakura-shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CANON KABUSHIKI KAISHA |
Tokyo |
|
JP |
|
|
Family ID: |
51207402 |
Appl. No.: |
14/147653 |
Filed: |
January 6, 2014 |
Current U.S.
Class: |
348/345 ;
359/557; 359/676 |
Current CPC
Class: |
G02B 15/177
20130101 |
Class at
Publication: |
348/345 ;
359/676; 359/557 |
International
Class: |
G02B 15/14 20060101
G02B015/14 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 22, 2013 |
JP |
2013-009114 |
Claims
1. A zoom lens, comprising, in order from an object side to an
image side: a first lens unit having a negative refractive power; a
second lens unit having a positive refractive power; and an
aperture stop disposed between the first lens unit and the second
lens unit, the aperture stop moving along a locus different from
loci of the first lens unit and the second lens unit during
zooming, the first lens unit and the second lens unit being
configured to change an interval between the first lens unit and
the second lens unit during zooming, the second lens unit including
at least one positive lens and at least one negative lens, wherein
the following conditional expression is satisfied:
0.40<Dsw/D2w<0.60, where Dsw represents a distance on an
optical axis from a lens surface closest to the object side in an
entire system to the aperture stop at a wide angle end, and D2w
represents a distance on the optical axis from the lens surface
closest to the object side in the entire system to a lens surface
closest to the object side in the second lens unit at the wide
angle end.
2. A zoom lens according to claim 1, wherein the aperture stop
moves along a locus convex toward an image side during zooming from
the wide angle end to a telephoto end.
3. A zoom lens according to claim 1, wherein the following
conditional expression is satisfied: -1.20<f2/f1<-0.70, where
f1 represents a focal length of the first lens unit, and f2
represents a focal length of the second lens unit.
4. A zoom lens according to claim 1, further comprising a flare cut
stop disposed on an image side of the second lens unit, wherein the
following conditional expression is satisfied:
2.50<Dss/fw<4.50, where Dss represents a distance on the
optical axis from the aperture stop to the flare cut stop at the
wide angle end, and fw represents a focal length of the entire
system at the wide angle end.
5. A zoom lens according to claim 1, further comprising a flare cut
stop disposed on an image side of the second lens unit, wherein the
following conditional expressions are satisfied:
0.800<.phi.fw/.phi.bw<1.400, and
0.500<.phi.Dw/fw<1.000, where .phi.fw represents an aperture
diameter of the aperture stop at the wide angle end, .phi.bw
represents an aperture diameter of the flare cut stop at the wide
angle end, .phi.Dw represents a diameter of a light beam that is
emitted from a point light source positioned at infinity on the
optical axis and enters the lens surface closest to the object side
at the wide angle end, and fw represents a focal length of the
entire system at the wide angle end.
6. A zoom lens according to claim 1, wherein the first lens unit
includes, in order from the object side to the image side, a
negative lens and a positive lens.
7. A zoom lens according to claim 1, wherein the second lens unit
is moved to have a component in a direction perpendicular to the
optical axis so as to move an imaging position in the direction
perpendicular to the optical axis.
8. A zoom lens according to claim 1, further comprising, on an
image side of the second lens unit, a third lens unit having a
positive refractive power which moves during zooming.
9. A zoom lens according to claim 1, wherein the zoom lens forms an
image on a solid-state image pickup element.
10. An image pickup apparatus comprising: a zoom lens; and an image
sensor configured to receive an image formed by the zoom lens, the
zoom lens comprising, in order from an object side to an image
side: a first lens unit having a negative refractive power; a
second lens unit having a positive refractive power; and an
aperture stop disposed between the first lens unit and the second
lens unit, the aperture stop moving along a locus different from
loci of the first lens unit and the second lens unit during
zooming, the first lens unit and the second lens unit being
configured to change an interval between the first lens unit and
the second lens unit during zooming, the second lens unit including
at least one positive lens and at least one negative lens, wherein
the following conditional expression is satisfied:
0.40<Dsw/D2w<0.60, where Dsw represents a distance on an
optical axis from a lens surface closest to the object side in an
entire system to the aperture stop at a wide angle end, and D2w
represents a distance on the optical axis from the lens surface
closest to the object side in the entire system to a lens surface
closest to the object side in the second lens unit at the wide
angle end.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a zoom lens, which is
suitable for an image pickup apparatus such as a digital still
camera, a video camera, a TV camera, or a monitoring camera.
[0003] 2. Description of the Related Art
[0004] In recent years, an image pickup apparatus (camera) such as
a video camera or a digital still camera using a solid-state image
pickup element has a smaller size and more sophisticated functions.
Further, along with the smaller size and more sophisticated
functions of the image pickup apparatus, an imaging optical system
used for the image pickup apparatus is required to be a small zoom
lens having a wide angle of field (photographing angle of field), a
large aperture ratio, and high optical performance. As a zoom lens
having a small entire system, a wide angle of field, and a large
aperture ratio, there is known a negative lead type zoom lens in
which a lens unit having a negative refractive power is positioned
in front (disposed closest to an object side).
[0005] Japanese Patent Application Laid-Open No. 2001-141997
discloses a three-unit zoom lens including, in order from the
object side to an image side, a first lens unit having a negative
refractive power, a second lens unit having a positive refractive
power, and a third lens unit having a positive refractive power, in
which an interval between the lens units is changed for zooming.
Japanese Patent Application Laid-Open No. 2001-141997 discloses a
zoom lens having a relatively small size and a larger aperture
ratio as an F-number of approximately 2.3 at a wide angle end
compared with an F-number of approximately 2.8 that is common in
conventional systems. In addition, Japanese Patent Application
Laid-Open No. 2008-065051 discloses a two-unit zoom lens including,
in order from the object side to the image side, a first lens unit
having a negative refractive power, and a second lens unit having a
positive refractive power, in which an interval between the lens
units is changed for zooming. Japanese Patent Application Laid-Open
No. 2008-065051 discloses a zoom lens that has achieved a large
aperture ratio as an F-number of approximately 1.4 at the wide
angle end.
[0006] In recent years, the zoom lens that is used for the image
pickup apparatus is strongly required to have a large aperture
ratio and high optical performance over the entire zoom range.
[0007] The negative lead type zoom lens described above can
relatively easily achieve a wider angle of field and a smaller size
of the entire system. However, because the entire lens system
becomes asymmetric with respect to the aperture stop, variations of
aberrations due to zooming become larger when the aperture ratio is
increased, and hence it is difficult to obtain high optical
performance over the entire zoom range. In order to achieve a
smaller size of the entire system and a larger aperture ratio in
the negative lead type two-unit zoom lens or three-unit zoom lens
described above, it is important to appropriately set a lens
structure of each lens unit constructing the zoom lens and a
position of the aperture stop disposed in an optical path.
[0008] For instance, it is important to appropriately set the lens
structure of the second lens unit and move the aperture stop for
zooming. When these structures are inappropriate, it becomes very
difficult to obtain high optical performance while achieving
downsizing of the entire system and a larger aperture ratio.
[0009] The three-unit zoom lens disclosed in Japanese Patent
Application Laid-Open No. 2001-141997 has an F-number of
approximately 2.3 at the wide angle end, which is not sufficient as
a larger aperture ratio. On the other hand, the two-unit zoom lens
disclosed in Japanese Patent Application Laid-Open No. 2008-065051
has a large aperture ratio as an F-number of approximately 1.4 at
the wide angle end, but downsizing thereof is not sufficient
because the first lens unit includes four lenses.
SUMMARY OF THE INVENTION
[0010] Therefore, the present invention provides a zoom lens having
a small size of the entire lens system, a large aperture ratio, and
high optical performance over the entire zoom range, and an image
pickup apparatus including the zoom lens.
[0011] According to one embodiment of the present invention, there
is provided a zoom lens including, in order from an object side to
an image side:
[0012] a first lens unit having a negative refractive power;
[0013] a second lens unit having a positive refractive power;
and
[0014] an aperture stop that moves along a locus different from
loci of the first lens unit and the second lens unit during
zooming, which is disposed between the first lens unit and the
second lens unit,
[0015] the first lens unit and the second lens unit being
configured to change an interval between the first lens unit and
the second lens unit during zooming,
[0016] the second lens unit including at least one positive lens
and at least one negative lens,
[0017] in which the following conditional expression is
satisfied:
0.40<Dsw/D2w<0.60
where Dsw represents a distance from a lens surface closest to the
object side in an entire system at a wide angle end to the aperture
stop, and D2w represents a distance from the lens surface closest
to the object side in the entire system at the wide angle end to a
lens surface closest to the object side in the second lens
unit.
[0018] Further features of the present invention will become
apparent from the following description of exemplary embodiments
with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is an optical cross-sectional view and movement loci
of lens units in a zoom lens of Embodiment 1 of the present
invention.
[0020] FIG. 2A is an aberration diagram at a wide angle end of the
zoom lens of Embodiment 1 of the present invention.
[0021] FIG. 2B is an aberration diagram at a telephoto end of the
zoom lens of Embodiment 1 of the present invention.
[0022] FIG. 3 is an optical cross-sectional view and movement loci
of lens units in a zoom lens of Embodiment 2 of the present
invention.
[0023] FIG. 4A is an aberration diagram at the wide angle end of
the zoom lens of Embodiment 2 of the present invention.
[0024] FIG. 4B is an aberration diagram at the telephoto end of the
zoom lens of Embodiment 2 of the present invention.
[0025] FIG. 5 is an optical cross-sectional view and movement loci
of lens units in a zoom lens of Embodiment 3 of the present
invention.
[0026] FIG. 6A is an aberration diagram at the wide angle end of
the zoom lens of Embodiment 3 of the present invention.
[0027] FIG. 6B is an aberration diagram at the telephoto end of the
zoom lens of Embodiment 3 of the present invention.
[0028] FIG. 7 is a schematic diagram of a main part of an image
pickup apparatus of the present invention.
DESCRIPTION OF THE EMBODIMENTS
[0029] Hereinafter, exemplary embodiments of the present invention
are described in detail with reference to the attached drawings. A
zoom lens of one embodiment of the present invention includes, in
order from an object side to an image side, a first lens unit
having a negative refractive power, and a second lens unit having a
positive refractive power, in which an interval between the lens
units is changed during zooming. The zoom lens further includes,
between the first lens unit and the second lens unit, an aperture
stop that moves along a locus different from loci of other lens
units during zooming. The zoom lens may further include, on the
image side of the second lens unit, a third lens unit having a
positive refractive power that moves during zooming.
[0030] FIG. 1 is a lens cross-sectional view at a wide angle end of
a zoom lens of Embodiment 1 of the present invention. FIGS. 2A and
2B are aberration diagrams of the zoom lens of Embodiment 1 at the
wide angle end and a telephoto end, respectively. The zoom lens of
Embodiment 1 has a zoom ratio of 3.62, an aperture ratio of 1.91 to
5.85, and a photographing half angle of field of 33.73 degrees at
the wide angle end.
[0031] FIG. 3 is a lens cross-sectional view at the wide angle end
of a zoom lens of Embodiment 2 of the present invention. FIGS. 4A
and 4B are aberration diagrams of the zoom lens of Embodiment 2 at
the wide angle end and the telephoto end, respectively. The zoom
lens of Embodiment 2 has a zoom ratio of 4.50, an aperture ratio of
1.86 to 6.07, and a photographing half angle of field of 33.39
degrees at the wide angle end.
[0032] FIG. 5 is a lens cross-sectional view at the wide angle end
of a zoom lens of Embodiment 3 of the present invention. FIGS. 6A
and 6B are aberration diagrams of the zoom lens of Embodiment 3 at
the wide angle end and the telephoto end, respectively. The zoom
lens of Embodiment 3 has a zoom ratio of 2.56, an aperture ratio of
1.87 to 3.80, and a photographing half angle of field of 32.67
degrees at the wide angle end.
[0033] FIG. 7 is a schematic diagram of a main part of an image
pickup apparatus of the present invention. The zoom lens of each
embodiment is an image taking lens system used for an image pickup
apparatus such as a video camera and a digital camera. In the lens
cross-sectional views, a left is a subject side (an object side)
(front), and a right is an image side (rear). In the lens
cross-sectional views, an order of the lens unit from the object
side is denoted by i, and the i-th lens unit is denoted by Li.
[0034] An aperture stop for restricting an F-number light beam is
denoted by SP. A flare cut stop for restricting a passing light
beam is denoted by FS. An optical block G corresponds to an optical
filter, a face plate, a quartz low pass filter, or an infrared cut
filter. On an image plane IP, there is set an image pickup surface
of a solid-state image pickup element (photoelectric conversion
element) such as a CCD sensor or a CMOS sensor in the case of use
as an image taking optical system for a video camera or a digital
still camera.
[0035] In the aberration diagrams, spherical aberration diagrams
illustrate for d-line and g-line. Astigmatism diagrams are shown
for meridional image plane denoted by .DELTA.M and for sagittal
image plane denoted by .DELTA.S. A lateral chromatic aberration is
represented for g line. A half angle of field (degree) is denoted
by co and an F number is denoted by Fno. Further, in the
embodiments described below, the wide angle end and the telephoto
end means zoom positions at which the zoom lens unit is positioned
at each end in the mechanically movable range on the optical
axis.
[0036] The zoom lens of each embodiment includes, in order from the
object side to the image side, a first lens unit L1 having a
negative refractive power, and a second lens unit L2 having a
positive refractive power. Further, an interval between the lens
units is changed during zooming.
[0037] The second lens unit L2 includes at least one positive lens
and at least one negative lens. The zoom lens further includes,
between the first lens unit L1 and the second lens unit L2, the
aperture stop SP that moves along a locus different from loci of
the first lens unit L1 and the second lens unit L2 during zooming.
With this structure, a larger aperture ratio can be easily achieved
while maintaining good optical performance even with a small number
of lenses.
[0038] In each embodiment, the following conditional expression is
satisfied:
0.40<Dsw/D2w<0.60 (1),
where Dsw represents a distance from a lens surface closest to the
object side in the entire system end to the aperture stop SP at the
wide angle, and D2w represents a distance from the lens surface
closest to the object side in the entire system to a lens surface
closest to the object side in the second lens unit L2 at the wide
angle end.
[0039] The zoom lens of each embodiment includes, in order to
shorten the entire lens length (distance from the first lens
surface to the image plane) so that a front lens diameter is
decreased, in order from the object side to the image side, the
first lens unit having a negative refractive power and the second
lens unit having a positive refractive power. Further, the second
lens unit L2 includes at least one positive lens and at least one
negative lens, and hence axial aberration and chromatic aberration
due to the larger aperture ratio are appropriately corrected.
[0040] The conditional expression (1) defines a position of the
aperture stop SP at the wide angle end. When a lower limit value of
the conditional expression (1) is exceeded, the aperture stop SP
becomes too far from the second lens unit L2 having a positive
refractive power so that peripheral light intensity becomes
insufficient. When an upper limit value of the conditional
expression (1) is exceeded, the aperture stop SP becomes too far
from the first lens unit L1 having a negative refractive power, and
hence it is necessary to increase a stop diameter in order to
decrease the F-number.
[0041] As a result, a lower line of an off-axial ray enters a
periphery of the lens at a steep angle so that flare is increased.
Therefore, in order to maintain good image quality, it is necessary
to increase the number of lenses of the first lens unit L1. Thus,
the lens system becomes large inappropriately.
[0042] In addition, the aperture stop SP is moved along the locus
different from loci of the lens units during zooming, so as to be
positioned at an appropriate position in the optical axis direction
at an intermediate zoom position. Further, because the aperture
stop SP can be moved so as not to interfere with the lens units on
the telephoto side, the aperture stop SP does not prevent movement
of the second lens unit L2 that is mainly in charge of zooming,
which facilitates downsizing of the entire lens length at the same
magnification. In each embodiment, it is more preferred to set the
value range of the conditional expression (1) as follows.
0.41<Dsw/D2w<0.60 (1a)
[0043] It is still more preferred to set the conditional expression
(1a) as follows.
0.50<Dsw/D2w<0.60 (1b)
[0044] In each embodiment, it is more preferred to satisfy one or
more of the following conditional expressions:
-1.20<f2/f1<-0.70 (2)
2.50<Dss/fw<4.50 (3)
0.800<.phi.fw/.phi.bw<1.400 (4)
0.500<.phi.Dw/fw<1.000 (5)
where f1 represents a focal length of the first lens unit L1 and f2
represents a focal length of the second lens unit L2. The zoom lens
includes a flare cut stop FS on the image side of the second lens
unit L2. Dss represents a distance from the aperture stop SP to the
flare cut stop FS at the wide angle end, and fw represents a focal
length of the entire system at the wide angle end. Further, .phi.fw
represents an aperture diameter of the aperture stop SP at the wide
angle end, .phi.bw represents an aperture diameter of the flare cut
stop FS at the wide angle end, and .phi.Dw represents a diameter of
a light beam that is emitted from a point light source positioned
at infinity on the optical axis and enters the lens surface closest
to the object side at the wide angle end.
[0045] Next, technical meanings of the above-mentioned conditional
expressions are described below.
[0046] The conditional expression (2) defines a preferred ratio
between the focal length of the first lens unit L1 and the focal
length of the second lens unit L2. When the lower limit value of
the conditional expression (2) is exceeded, refractive power of the
second lens unit L2 becomes too small, and hence much spherical
aberration or coma is generated inappropriately from the second
lens unit L2. When the upper limit value of the conditional
expression (2) is exceeded, an absolute value of the negative focal
length of the first lens unit L1 becomes too large. Therefore, it
becomes difficult to correct field curvature or the like generated
in the first lens unit L1 without adding a lens, which is not good.
It is more preferred to set the value range of the conditional
expression (2) as follows.
-1.10<f2/f1<-0.70 (2a)
[0047] It is still more preferred to set the conditional expression
(2a) as follows.
-1.10<f2/f1<-1.00 (2b)
[0048] The conditional expression (3) defines a preferred position
of the flare cut stop FS in the optical axis direction. When the
lower limit value of the conditional expression (3) is exceeded,
the flare cut stop FS becomes too close to the aperture stop SP.
Therefore, it becomes difficult to effectively suppress flare on an
upper line of the off-axial ray that is apt to be deteriorated by a
larger aperture ratio. When the upper limit value of the
conditional expression (3) is exceeded, peripheral light intensity
is rapidly decreased inappropriately. It is more preferred to set
the value range of the conditional expression (3) as follows.
2.90<Dss/fw<4.10 (3a)
[0049] The conditional expression (4) defines a preferred ratio
between an aperture diameter of the aperture stop SP disposed
between the first lens unit L1 and the second lens unit L2 at the
wide angle end, and the aperture diameter of the flare cut stop FS
disposed on the image side of the second lens unit L2 at the wide
angle end. When the lower limit value of the conditional expression
(4) is exceeded, the aperture diameter of the flare cut stop FS
becomes too large so that it becomes difficult to sufficiently
suppress flare on the upper line of the off-axial ray.
[0050] For this reason, it becomes difficult to correct the flare
without adding a lens to the second lens unit L2 and a lens on the
image side of the second lens unit L2. When the upper limit value
of the conditional expression (4) is exceeded, a stop diameter of
the aperture stop SP becomes too large. Therefore, it becomes
difficult to sufficiently suppress the flare on the lower line. For
this reason it becomes difficult to correct the flare without
adding a lens to the second lens unit L2 and a lens on the object
side of the second lens unit L2.
[0051] The conditional expression (5) defines a preferred diameter
of an axial light beam with respect to a focal length of the entire
system at the wide angle end. When the lower limit value of the
conditional expression (5) is exceeded, it is advantageous for
optical performance but obtained light intensity becomes small
because the diameter of the axial light beam is too small.
Therefore, it becomes difficult to achieve a larger aperture ratio.
When the upper limit value of the conditional expression (5) is
exceeded, the diameter of the axial light beam becomes too large.
Therefore, it becomes difficult to obtain good imaging performance
over the entire range of the light beam without increasing the
number of lenses. It is more preferred to set the value ranges of
the conditional expressions (4) and (5) as follows.
0.900<.phi.fw/.phi.bw<1.250 (4a)
0.500<.phi.Dw/fw<0.600 (5a)
[0052] As described above, according to each embodiment, it is
possible to provide a zoom lens having a small number of lenses, a
small size of the entire system, and a large aperture ratio as an
F-number of 2.0 or smaller that is one step smaller than a hitherto
common zoom lens having an F-number of approximately 2.8 so as to
sufficiently obtain the effect of the larger aperture ratio.
[0053] Next, an exemplary lens structure of each embodiment is
described. It is preferred that the aperture stop SP move along a
locus convex toward an image side when zooming from the wide angle
end to the telephoto end. Thus, even when the F-number is changed
to have a larger aperture ratio at the wide angle end, it becomes
easy to effectively suppress flare on the lower line of a light ray
at an intermediate image height while maintaining peripheral light
intensity at an intermediate zoom position.
[0054] It is preferred to set a lens surface of the second lens
unit L2 closest to the object side to be an aspherical surface.
This is because, with this structure, it is possible to effectively
correct spherical aberration and coma that are apt to be
deteriorated by a larger aperture ratio at a relatively large
height from the optical axis of the axial light beam. It is
preferred to constitute the first lens unit L1 to include, in order
from the object side, a negative lens and a positive lens. This is
because, with this structure, lateral chromatic aberration and
field curvature can be effectively corrected so that the lens
structure can be simplified and downsized.
[0055] It is preferred to move the second lens unit L2 to have a
component in a direction perpendicular to the optical axis so that
an imaging position is moved in the direction perpendicular to the
optical axis. With this structure, it becomes easy to effectively
perform vibration isolation.
[0056] Next, lens structures of the embodiments are described. The
zoom lenses of Embodiments 1 and 2 are three-unit zoom lenses
constituted of three lens units including, in order from the object
side to the image side, the first lens unit L1 having a negative
refractive power, the second lens unit L2 having a positive
refractive power, and the third lens unit L3 having a positive
refractive power. Further, during zooming from the wide angle end
to the telephoto end, as illustrated by the arrows in the lens
cross-sectional views, the first lens unit L1 moves along a locus
convex toward an image side, the second lens unit L2 moves toward
the object side, and the third lens unit L3 moves.
[0057] The aperture stop SP moves toward the object side along a
locus different from loci of other lens units. The zoom lenses of
Embodiments 1 and 2 perform main zooming by moving the second lens
unit L2 and correct a movement of the image plane due to zooming by
moving the first lens unit L1 along a locus convex toward the image
side. In addition, telecentric imaging on the image side, which is
necessary for an image pickup apparatus using a solid-state image
pickup element in particular, is achieved by permitting the third
lens unit L3 to have a role of a field lens. In addition, the flare
cut stop FS is disposed on the image side of the second lens unit
L2.
[0058] The zoom lens of Embodiment 3 is a two-unit zoom lens
constituted of two lens units including, in order from the object
side to the image side, the first lens unit L1 having a negative
refractive power, and the second lens unit L2 having a positive
refractive power. Further during zooming from the wide angle end to
the telephoto end, as illustrated by the arrows in the lens
cross-sectional view, the first lens unit L1 moves along a locus
convex toward an image side, and the second lens unit L2 moves
toward the object side. The aperture stop SP moves toward the
object side along a locus different from loci of the other lens
units.
[0059] The zoom lens of Embodiment 3 performs main zooming by
moving the second lens unit L2 and corrects movement of the image
plane due to zooming by moving the first lens unit L1 along a locus
convex toward the image side. In addition, the flare cut stop FS is
disposed on the image side of the second lens unit L2. This flare
cut stop FS cuts a harmful light ray (flare light) that
deteriorates optical performance.
[0060] In each embodiment, the first lens unit L1 having a negative
refractive power is constituted of two lenses including, in order
from the object side to the image side, a negative lens G11 and a
positive meniscus lens G12 having a convex surface on the object
side. In addition, the negative lens G11 of the first lens unit has
aspherical lens surfaces on both the object side and the image
side. With this lens structure, lateral chromatic aberration and
field curvature are appropriately corrected by a minimum number of
lenses.
[0061] The second lens unit L2 includes, in order from the object
side to the image side, a positive lens G21 having a convex surface
on the object side, a cemented lens in which a positive lens G22
having a convex surface on the object side and a negative lens G23
having a concave surface on the image plane side are cemented, and
a positive lens G24. By using a lens surface having an aspherical
shape for the positive lens G21 disposed closest to the object
side, spherical aberration and coma are appropriately corrected.
With this lens structure, spherical aberration and coma increased
by the larger aperture ratio are appropriately corrected by a small
number of lenses.
[0062] In Embodiments 1 and 2, the third lens unit L3 is
constituted of a single positive lens. Thus, a thin profile of the
entire lens system is realized, and quick focusing is facilitated
by moving the small and lightweight third lens unit in the optical
axis direction. Each numerical embodiment of each embodiment
described later shows a case where an object at infinity is
focused. One or more aspherical lenses may be added to each lens
unit in order to suppress aberration of the off-axial ray more
appropriately.
[0063] The aperture area of the aperture stop SP may be variable or
fixed. Even in the case where the aperture area is fixed, it is
possible to obtain a desired F-number at positions other than the
wide angle end by appropriately performing the movement during
zooming.
[0064] Referring to FIG. 7, a digital still camera according to an
embodiment of the present invention is described as an image pickup
apparatus using the zoom lenses of the present invention as image
taking optical systems.
[0065] In FIG. 7, the digital still camera includes: a camera main
body 20; an image taking optical system 21 including any one of the
zoom lenses of Embodiments 1 to 3; and a solid-state image pickup
element (photoelectric conversion element) 22 such as a CCD sensor
and a CMOS sensor, which is built in the camera main body to
receive a subject image formed by the image taking optical system
21.
[0066] Applying the zoom lens of the present invention to a digital
still camera as described above enables realization of a compact
and high optical performance image pickup apparatus. Further, the
zoom lens of each embodiment can be used also for a digital video
camera or a projection optical system of a projection apparatus
(projector).
[0067] Numerical embodiments 1 to 3 corresponding to Embodiments 1
to 3 of the present invention are described below. Each numerical
embodiment shows order i of surfaces from the object side. A
curvature radius of a lens surface is denoted by ri, an interval
between an i-th surface and an (i+1)-th surface is denoted by di. A
refractive index and an Abbe constant of an optical member
interposed between the i-th surface and the (i+1)-th surface for a
d-line are denoted ndi and .nu.di, respectively. The aspherical
shape can be expressed by the following equation:
X=(h.sup.2/R)/[1+{1-(1+k)(h/R).sup.2}].sup.1/2+A4h.sup.4+A6h.sup.6+A8h.s-
up.8+A10h.sup.10+A12h.sup.12,
where X represents a displacement in the optical axis direction at
a position having a height h from the optical axis with respect to
the vertex of surface, k represents a conic constant, A4, A6, A8,
A10, and A12 represent aspherical coefficients of fourth, sixth,
eighth, tenth, and twelfth orders, respectively, and R represents a
paraxial curvature radius. In addition, "e-X" means
".times.10.sup.-x". Further, a relationship between the
above-mentioned each conditional expression and each Numerical
embodiment is shown in Table 1.
[0068] A value of an interval d5 is negative at the intermediate
zoom position and at the telephoto end in Numerical embodiment 3
because the aperture stop SP and the second lens unit L2 are
counted in this order. Back focus BF represents an air-equivalence
length from the final lens surface to a paraxial image plane. Note
that, unless otherwise particularly described, the unit of the
length is mm.
Numerical Embodiment 1
TABLE-US-00001 [0069] Unit mm Surface data Surface number r d nd
.nu.d 1* -89882.247 1.10 1.84954 40.1 2* 5.480 2.21 3 10.461 1.60
1.94595 18.0 4 21.049 (Variable) 5 SP .infin. (Variable) 6* 6.649
2.30 1.74330 49.3 7* 195.770 0.17 8 5.668 1.65 1.51633 64.1 9
40.094 0.50 1.80518 25.4 10 3.904 2.64 11 12.109 1.40 1.72000 50.2
12 397.545 0.29 13 FS .infin. (Variable) 14 13.220 1.70 1.48749
70.2 15 -333.999 (Variable) 16 .infin. 0.84 1.51633 64.1 17 .infin.
0.50 Image plane .infin. Aspherical surface data First surface K =
-7.54512e+008 A4 = -2.24468e-004 A6 = 6.41337e-006 A8 =
-5.15297e-008 A10 = -2.13056e-010 Second surface K = -2.26664e+000
A4 = 9.33605e-004 A6 = -2.01163e-005 A8 = 9.37294e-007 A10 =
-1.63131e-008 Sixth surface K = -1.20723e-001 A4 = -1.07870e-004 A6
= 1.70602e-006 A8 = 7.62863e-008 A10 = 1.71340e-008 Seventh surface
K = 2.32795e+003 A4 = 1.21576e-004 A6 = 2.00095e-006 A8 =
6.73308e-007 A10 = -1.26149e-008 Various data Zoom ratio 3.62 Focal
length 5.05 10.29 18.25 F-number 1.91 4.09 5.85 Half angle of field
(degree) 33.73 20.63 11.99 Image height 3.37 3.88 3.88 Total lens
length 38.51 35.93 42.02 BF 3.95 3.85 3.70 d4 3.50 5.28 1.42 d5
11.50 0.50 0.50 d13 3.34 10.13 20.32 d15 2.90 2.80 2.65 Zoom lens
unit data Unit First surface Focal length 1 1 -10.50 2 6 10.82 3 14
26.13 Stop diameter data Surface Diameter 5 4.750 13 5.022
Numerical Embodiment 2
TABLE-US-00002 [0070] Unit mm Surface data Surface number r d nd
.nu.d 1* -18269.953 1.40 1.84954 40.1 2* 6.572 2.63 3 12.205 1.90
1.94595 18.0 4 23.900 (Variable) 5 SP .infin. (Variable) 6* 7.891
2.53 1.74330 49.3 7* -7208.564 0.20 8 7.614 2.08 1.51633 64.1 9
66.773 0.60 1.80518 25.4 10 4.878 3.34 11* 13.082 1.37 1.72903 54.0
12* 97.028 0.65 13 FS .infin. (Variable) 14 15.814 2.00 1.48749
70.2 15 -389.408 (Variable) 16 .infin. 1.00 1.51633 64.1 17 .infin.
0.50 Image plane .infin. Aspherical surface data First surface K =
-7.54512e+008 A4 = -1.20558e-004 A6 = 2.58721e-006 A8 =
-1.74608e-008 A10 = -3.44159e-011 A12 = 2.21099e-013 Second surface
K = -2.20089e+000 A4 = 5.40013e-004 A6 = -7.50127e-006 A8 =
2.50859e-007 A10 = -3.14999e-009 A12 = -1.11406e-012 Seventh
surface K = -1.58177e-001 A4 = -7.62268e-005 A6 = 6.05648e-007 A8 =
2.00021e-008 A10 = -2.05644e-011 A12 = 6.78844e-011 Eighth surface
K = -8.54977e+004 A4 = 8.43187e-005 A6 = 1.02155e-006 A8 =
1.40331e-007 A10 = -4.26243e-009 A12 = 9.55445e-011 Twelfth surface
K = 1.33928e+000 A4 = 1.25785e-004 A6 = 2.13654e-007 A8 =
-1.00957e-006 A10 = 3.50066e-007 A12 = -3.05955e-008 Thirteenth
surface K = -6.16286e+002 A4 = 3.17627e-004 A6 = 5.27720e-006 A8 =
-9.40691e-007 A10 = 1.90350e-007 A12 = -1.75687e-008 Various data
Zoom ratio 4.50 Wide angle Intermediate Telephoto Focal length 6.18
12.53 27.80 F-number 1.86 3.71 6.07 Half angle of field 33.39 20.27
9.45 (degree) Image height 4.07 4.63 4.63 Total lens length 45.65
42.78 60.52 BF 4.74 3.82 7.48 d4 7.93 7.01 0.34 d5 9.50 0.50 0.50
d13 3.99 12.91 31.22 d15 3.58 2.66 6.32 Zoom lens unit data Unit
First surface Focal length 1 1 -12.58 2 6 12.97 3 14 31.22 Stop
diameter data Surface Diameter 5 6.700 13 5.500
Numerical Embodiment 3
TABLE-US-00003 [0071] Unit mm Surface data Surface number r d nd
.nu.d 1* -3205.929 1.10 1.84954 40.1 2* 5.987 1.70 3 9.716 1.60
1.92286 18.9 4 20.076 (Variable) 5 SP .infin. (Variable) 6* 6.047
2.30 1.74330 49.3 7* 146.498 0.15 8 5.899 1.65 1.51633 64.1 9
-34.497 0.50 1.80518 25.4 10 3.904 1.50 11 11.336 1.50 1.77250 49.6
12 -19.834 0.29 13 FS .infin. (Variable) 14 .infin. 0.84 1.51633
64.1 15 .infin. 0.50 Image plane .infin. Aspherical surface data
First surface K = -7.54512e+008 A4 = -3.33905e-004 A6 =
8.22959e-006 A8 = -5.13009e-008 A10 = -2.13056e-010 Second surface
K = -2.57568e+000 A4 = 9.05690e-004 A6 = -1.99981e-005 A8 =
9.37294e-007 A10 = -1.63131e-008 Seventh surface K = -1.93219e-001
A4 = -2.75397e-004 A6 = 4.99940e-006 A8 = -2.07666e-007 A10 =
-1.57616e-008 A12 = 7.43750e-009 Eighth Surface K = 1.19672e+003 A4
= 1.58244e-007 A6 = -1.07394e-005 A8 = 1.35072e-006 A10 =
9.21810e-008 A12 = 3.27632e-009 Various data Zoom ratio 2.56 Wide
angle Intermediate Telephoto Focal length 5.26 9.94 13.45 F-number
1.87 3.28 3.80 Half angle of field 32.67 21.30 16.07 (degree) Image
height 3.37 3.88 3.88 Total lens length 31.48 25.36 25.10 BF 6.69
10.03 12.54 d4 5.00 3.53 0.76 d5 7.50 -0.50 -0.50 d13 5.64 8.98
11.49 Zoom lens unit data Unit First surface Focal length 1 1
-12.16 2 6 8.68 Stop diameter data Surface Diameter 5 4.750 13
5.000
TABLE-US-00004 TABLE 1 Conditional Expression Embodiment 1
Embodiment 2 Embodiment 3 (1) Dsw/D2w 0.422 0.593 0.556 (2) f2/f1
-1.031 -1.031 -0.714 (3) Dss/fw 4.051 3.279 2.929 (4)
.PHI.fw/.phi.bw 0.946 1.218 0.950 (5) .phi.Dw/fw 0.524 0.538
0.535
[0072] While the present invention has been described with
reference to exemplary embodiments, it is to be understood that the
invention is not limited to the disclosed exemplary embodiments.
The scope of the following claims is to be accorded the broadest
interpretation so as to encompass all such modifications and
equivalent structures and functions.
[0073] This application claims the benefit of Japanese Patent
Application No. 2013-009114, filed Jan. 22, 2013, which is hereby
incorporated by reference herein in its entirety.
* * * * *